The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Motor vehicle transmissions are often divided into two distinct classes: manual transmissions and automatic transmissions. Manual transmissions typically have a plurality of operator selected gears and a manual (foot operated) clutch whereas automatic transmissions sequence gear selection and clutch operation, generally without active operator involvement.
A recent addition to the transmission repertoire combines elements of both manual and automatic transmissions: the dual clutch transmission or DCT. The dual clutch transmission utilizes meshing pairs of gears and synchronizer clutches much like a manual transmission but with a pair of friction clutches. Because selection and engagement of gears and clutch are typically under the control of an electronic control system (a transmission control module or TCM), the dual clutch transmission essentially functions as an automatic transmission.
The meshing gears are arranged in a dual clutch transmission such that alternating gears in an upshift (or downshift) sequence, e.g., first, third and fifth, are associated with one of the two clutches and the interleaved, alternating gears, e.g., second, fourth and sixth are associated with the other clutch. In this way, while one gear and clutch is engaged and operating, for example, second gear, the next higher gear in an upshift sequence, for example third, is being synchronized and connected to a driveshaft so that the actual shift from second to third involves essentially simply disengaging the one clutch and engaging the other clutch.
This shift sequence of dual clutch transmissions provides very rapid adjacent gear upshifts and downshifts and is one of the most desirable and appreciated features of this transmission type. Shift times of about 200 milliseconds or less are achievable by such transmissions.
In order to achieve such reduced shift sequence times, it is necessary that, among other considerations, clutch travel must be reduced to a minimum. It can readily be appreciated that excessive clutch pre-travel, i.e., travel of the clutch actuator and linkage from a released position to an applied position simply delays a desired clutch and transmission action. Moreover, as the clutch facing material wears, the pre-travel will increase, thus effectively further slowing the response time of the clutch. Accordingly, it is highly desirable to configure both a single and a dual clutch transmission clutch to reduce pre-travel and provide optimum clutch response time. The present invention is so directed.